What is one reason that the community had to change the climate or landscape?

Jonas's community is completely uniform, comfortable, structured, and safe. The entire community operates on a concept referred to as Sameness, which prevents the citizens from experiencing the negative aspects of humanity at the expense of sacrificing individuality, excitement, wonder, and spontaneity.
In chapter 11, the Giver shares a memory of sled-riding down a snowy hill with Jonas, who enjoys the thrilling experience. After Jonas receives the memory, he asks the Giver what happened to snow and hills. The Giver goes on to explain that long ago the community's scientists altered the climate in order to prevent snow from falling because it was not advantageous to agricultural production. The Giver also explains to Jonas that there are no longer hills in the community because it made transportation difficult and slowed down conveyance. The concept of Sameness made challenging landscapes and unpredictable weather obsolete so that life could be more uniform, safe, and efficient in the "utopian" community.